Simple battles I do Theater of the Mind, both live and remote.
In-person I use both my trusty 20+ year old Chessex wet-erase maps, I have a metric ton of 4e "Dungeon tiles", and while I don't use them to do whole maps (takes too long to set up, too easy to bump into one and have a chain reaction of mess-up), I do bring whatever set(s) for the terrains I am DMing and use them as additional detail. Look, trees, fallen logs, dense shrubs, etc. Tossed out randomly instead of drawn randomly.
A DMing trick I've used more than once for wilderness ambushes by the party is to draw basic terrain on the battlemap, and based on their skill check for picking a good spot to ambush I let them determien where they will start/where the foes will be comign from, and then give them various amounts of Dungeon Tiles wilderness terrain to place, based on how well they did their skill checks.
Also if I'm doing a complicated indoor battlemap I have a number of easel-sized 1" grid pads that my company got rid of when we closed a location. They used them for meetings, I use them to pre-draw complicated maps to not slow down the game.
Online if needing a battlemap there are so many places that either give it away for free or for a small Patron donation, it's dirty easy to get good quality battlemaps. Though I admit I don't bother with VTTs myself, and just throw it up in a Google Draw where everyone has edit access. I play in games with Roll20, and we always have technical problems, or the DM expecting we can see things that can't that require us to redo things, or suddenly seeing all of the monsters on a map so we know where everything is and have to pretend we don't.
(If you couldn't tell, only having 3 choices in the poll was hard for me.